Amanda Bynes allegedly set fire to a California neighbor’s driveway — along with her own clothing — prompting a forced psychiatric evaluation, authorities said.

The troubled actress, 27, allegedly lit the blaze in front of a small house in Thousand Oaks, Calif., at around 8:40 p.m. on Monday, sources told The Post.

A driver first spotted the actress on the ground — with her pants on fire.

“It’s dark, it’s 8:45 and I just see her laying down, stomach up and her pant legs on fire, a trail of, you know, fire and gas, and I pull over,” said witness Andrew Liverpool. In this case, no charges were filed.